Optical fiber switch having a movable fiber secured to a slide which is indirectly moved by a magnetic armature

ABSTRACT

An optical fiber switch comprising a fixed holder supporting a plurality of parallel fibers and a slide supporting a plurality of movable fibers having ends facing the ends of the fixedly mounted fibers. The slide is movable between first and second abutments in response to the activation of a magnetically activated armature. A first spring acts on the slide to displace it from the first abutment to the second abutment and a second stronger spring acts on the slide in opposition to the first spring. The armature carries an armature bracket which bears against the second spring to displace the second spring away from the slide when the armature is activated in order to diminish the action of the second spring so that the slide is displaced to the second abutment substantially only under the action of the first spring.

FIELD OF THE INVENTION

The present invention relates to an optical fibre switch containingoptical fibre conductors for switching optical signals from a firstplurality of parallel fibres to a second plurality of parallel fibres.Such a switch may be used as a relay, for example, in a loop system atthe connection point between the fibre loop and the bus terminal.

BACKGROUND

In optical fibre switch described in the Swedish patent application No.8204085.8 there is shown a movable slide to which the optical fibres areattached. The fibres run parallel to a fixed holder in the switch. Fibreends having the same properties and dimensions as those in the movableslide are fixedly arranged at the switching point. The movable slide isactuated by a movable armature in an electromagnetic iron circuit forproviding the switching action, and the movable slide is returned to itsneutral position in an unactuated state by a return spring.

SUMMARY OF THE INVENTION

In the known switch, direct actuation of the movable slide is achievedby an actuation arm provided with a spring tongue moving the slide underthe action of a magnetic force from one position to the other. Inpractice there are problems with this direct actuation, however, sincethe tongue of the actuating arm should be stiff at the beginning of themovement but weak at the end of it to withstand pressure without theaction of an unnecessarily large magnetic force.

The object of the present invention is to solve the above-mentionedproblem by providing an actuation means in an optical fibre relay whichhas an indirect action on the movable slide.

In accordance with the invention there is provided an optical fiberswitch comprising a fixed holder, at least one fixedly mounted fiber onsaid holder, a slide, at least one movable fiber secured to said slidein facing relation to said fixedly mounted fiber, first and secondabutments between which said slide is movable, and means including amagnetically activated armature for displacing said slide to selectivelyand controllably couple and uncouple said fibers optically, said meansincluding a rigidly clamped first spring acting on said slide todisplace the slide from said first abutment to said second abutment, asecond spring acting on said slide in opposition to said first spring,said second spring being stronger than said first spring, and meansrigidly mounted on said armature for diminishing the action of saidsecond spring on said slide, upon activation of said armature, so thatsaid slide is displaced to said second abutment substantially only underthe action of said first spring.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail with reference to theaccompanying drawings, in which:

FIG. 1 shows a known optical fibre switch in accordance with the abovementioned Swedish patent application,

FIGS. 2A and 2B diagrammatically illustrate optical fibers of the switchfor two respective positions;

FIG. 3 is a schematic diagram of the slide movement;

FIG. 4 shows a switch with indirect actuation in accordance with thepresent invention;

FIG. 5 is the detail view of a switch with indirect actuation accordingto FIG. 4; and

FIG. 6 is a sectional view taken along line 4--4 in FIG. 5.

DETAILED DESCRIPTION OF BEST MODES FOR CARRYING OUT THE INVENTION

FIG. 1 shows the optical fibre switch according to the above mentionedSwedish patent application, in the form of a relay. The relay isconstructed on a bottom plate 1 along the long side of which two ironcores 2 and 3 are attached. An armature 4 of soft, magnetic material isattached to an armature spring 5. Magnetic flux is generated in a mannerknown per se, with the aid of an unillustrated coil which magnetizes aniron circuit in which the magnetic cores 2, 3 and the armature 4 areincluded.

A holder 12 is attached to the bottom plate. The holder has threeoptical fibres 13, 14 and 15 fixed thereon. A movable slide 8 can movein a movement substantially perpendicularly to the longitudinaldirection of the fibres 13, 14, 15. Three optical fibres 19, 20 and 21are fixed to the slide 8. These fibres extend to the right in thefigure, past the right end edge of the slide, and are anchored in afixed holder 16. A return spring 17 keeps the movable slide 8 in placein its starting position in which the slide is pressed against the core2. On magnetizing, the movable slide is moved into engagement with theguide plate 10 against the surface 11 thereof.

In the described relay, as well as in similar structures for opticalfibre switching, it is normal that the armature 4 directly actuates themovable slide. When a armature 4, on operation, moves towards the core2, the spring tongue 7 will approach the movable slide 8 and when thetongue meets the slide the tongue will first flex a given distance inresponse to the inertia of the slide 8 and the spring bias in the returnspring 7, and will substantially begin to push the movable slide 8 untilthe latter is stopped by the surface 11. When the armature 4 thencontinues its movement into full engagement against the core 2, thespring tongue 7 is forced to deflect further.

In an optical fibre relay for switching, the movement of the fibrecarrying slide will be determined by the spacing between the fibres.

For the known relay according to the above, FIG. 2 illustrates thespacing D and the distance E which the movable slide moves when therelay is operated, and the distance E must in principle be equal to D inorder that the center lines of the fibres will coincide before and afterthe movement. FIG. 3 schematically illustrates the distance E and thedistance the armature suitably moves, namely H, which is equal to E+F+G,where the additional distance F designates play or lost motion in thearmature before the movable slide is actuated. The distance F may besaid to be necessary to allow armature bounce when the relay is releasedwithout affecting the slide giving the optical connection. The distanceG is the play or lost motion of the armature in the make state whichensures that minor dimensional inaccuracies do not affect the opticalconnection. The distances G and F contribute to the reliable function ofthe relay, and in practice they are small in relation to the necessarymovement E.

Some form of spring means must be employed to provide the lost motionscorresponding to distances G and F for a directly actuating armature. InFIG. 1, this spring means is the spring tongue 7. In a practicalembodiment there is an opposed relationship, however, since the tongue 7should be stiff at the beginning of the movement so that the lost motioncorresponding to F will not be large and thus require a large armaturestroke. On the other hand, at the termination of the stroke, the tongueshould be weak, so as to withstand pressure without the force increasingtoo much. The present invention has been conceived to solve thisproblem.

An indirect operating optical fibre switch, in accordance with theinvention, is illustrated in FIGS. 4, 5 and 6. A make spring 26 attachedto a core 23 is biassed so that it applies to the movable slide 28,corresponding to the slide 8 in the known relay, a force P₁ of the orderof magnitude 150 mN. A break spring 27 attached to a guide plate 40 isbiassed so that it applies to the movable slide 28 a force P₂ of theorder of magnitude 300 mN. The resultant P₂ -P₁ will be about 150 mN andconstitutes the force which in a release state keeps the movable slide28 against a core 22 corresponding to the core 2 in FIG. 1.

The complete appearance of the armature bracket 29 is illustrated inFIGS. 5 and 6, this only being partially apparent from FIG. 4. In FIG.5, the armature 24 is provided with the armature bracket 29 which uponthe make action acts on the break spring 27, via an adjustable tongue32, thus moving the spring 27 downwards. Thereby, the make spring 26 caninfluence the movable slide 28 so that it executes its movements andreaches its stop against the arresting surface 31 of the guide plate 30.The make spring 26 keeps the movable slide 28 presses against the stopsurface 31. The armature 24 can continue its movement until it isarrested by the pole boss 35.

The forces acting on the armature in this indirectly driven coupling inthe make state are:

during the first part distance F (see FIG. 3), only the counter directedforce (about 100 mN) of the armature spring 25.

During the next distance E, the break state spring 27 (about 300 mN)also acts on the armature opposite to the direction of movement, and themake state, spring 26 (about 150 mN) acts on the armature in thedirection of movement, which means that the armature during thisdistance must overcome a force of about 100+300-150=250 mN. When themovable slide has been arrested against the stop surface 31, thereremains the part distance G of the armature movement. During this partdistance G the armature is acted on by the armature spring 25 plus thebreak state spring 27, i.e. about 100+300=400 mN.

The construction of the inventive relay is not limited to the use of aleaf spring 26 as the make spring for the fibres. It is also possible topretension the fibres 19, 20, 21 at the holder 36 so that a biassingspring force occurs in the fibres themselves. The spring 27 will thenact with a counter force on one or all of the fibres 19, 20, 21.

By the indirect action on the movable slide described herein thefollowing advantages are afforded:

The slide 28 is acted on by the make state spring 26 immediately whenthe armature tongue actuates the break state spring 27 since thearmature bracket tongue 32 is stiff. This means that the lost motion Fcan be made short.

The lost motion F can be adjusted by bending the tongue 32.

During the armature travel G the force which is to be overcome is onlythat of the return force in the armature spring 25 and the release statespring 27.

The lost motion G is adjusted by bending the armature bracket tongue 33.

The armature stroke can be made less, with this indirectly drivencoupler than with a direct driven coupler, which requires resilientarmature tongue 7.

In the make state, the oscillating system (the slide 28 with its fibresand the spring 27) is disengaged from the armature 24 with itsrelatively large mass, whereby the damping time for the vibrationsoccurring at the operation state will be shortened.

In the manufacture of optical fibre relays according to the inventiondescribed, the adjustment of the relay function data is facilitated inthe following manner:

The armature with mounted armature spring 25 can be checked to assurethat it provides the proper force, and, if necessary, it can be adjustedbefore attachment to the core 23. The break state spring 26, which ismounted on the core 23, can be checked to assure that it provides theproper force and it can also be adjusted, if necessary, before mountingof the slide 28 and the other guides associated with the fibres. Thebreak state spring 27 which is mounted on its holder 40 can also bechecked to assure it provides the right force and it can also beadjusted, if necessary, before mounting the holder in the relay. Byvirtue of the capability of separately adjusting the component springs25, 26, 27 in the described manner, no operations are needed after theparts of the relay have been fitted in place the the risk of damagingthe delicate fibre ends in thus considerably reduced. In respect of thearmature 24, the method used for the springs has its counterpart in ameasurement check and possible adjustment beforehand of the twoadjusting tongues 32 and 33. In order for the movable slide 28 to beguided by a bottom plate 41 in its movement, the fixed fibre holder 36is provided with two wire springs 37, 38 which apply a force on theslide 28 directed towards the bottom plate 41 and which springs slide ingrooves in the slide 28 when the slide 28 moves.

What is claimed is:
 1. An optical fiber switch comprising a fixedholder, at least one fixedly mounted fiber on said holder, a slide, atleast one movable fiber secured to said slide in facing relation to saidfixedly mounted fiber, first and second abutments between which saidslide is movable, and means including a magnetically activated armaturefor displacing said slide to selectively and controllably couple anduncouple said fibers optically, said means including a rigidly clampedfirst spring acting on said slide to displace the slide from said firstabutment to said second abutment, a second spring action on said slidein opposition to said first spring, said second spring being strongerthan said first spring, and means rigidly mounted on said armature fordiminishing the action of said second spring on said slide, uponactivation of said armature, so that said slide is displaced to saidsecond abutment substantially only under the action of said firstspring.
 2. An optical fiber switch as claimed in claim 1 wherein saidmeans for diminishing the action of said second spring on said slidecomprises an armature bracket secured to said armature and including atongue positioned to engage said second spring to displace said secondspring in a direction away from said slide when the armature isactivated.
 3. An optical fiber switch as claimed in claim 2 wherein saidtongue is adjustable by bending to control its engagement with saidsecond spring.
 4. An optical fiber switch as claimed in claim 1 whereinsaid armature is displaceable and includes a tongue for engaging saidabutments to determine the extend of displacement of the armature.
 5. Anoptical fiber switch as claimed in claim 4 wherein said tongue isadjustable by bending.
 6. An optical fiber switch as claimed in claim 1wherein at least one of said springs is a leaf spring.
 7. An opticalfiber switch as claimed in claim 1 comprising guide means for guidingthe slide in its movement between said abutments.
 8. An optical fiberswitch as claimed in claim 7 wherein said guide means includes a guidehaving a guide surface against which said slide is movable and springmeans for urging said slide against said guide surface.